The majority of modern wind turbines generators presently in operation worldwide, utilize horizontal axis, large diameter, axial flow, propeller type wind turbine rotors. Typical aerodynamic efficiencies of these turbines based on frontal area with rotor diameter of ˜230 feet are in range of 28 to 30 percent. With a wind velocity of 14 meter per second (about 31 mph) the tangental blades tip velocity is typically in the range of 270 feet per second. At those velocities, the noise level generated by the turbine blades is substantial. For this reason, many manufacturers recommend a distance of several hundred meters between turbines and residential housing. Typical power output of these utility size turbine generators (such as General Electric's Model GE1.5) is about 1500 kW.
Smaller wind turbines of the same type are being used for broad range of applications, such as utility bill reduction and battery charging. Typically, the blade diameters of these turbines range in sizes of 7 to 9 meters (23 to 30 feet) and have power output of about 10 kW to 20 kW at rated 14 m/s wind velocities. Blade tip velocities are about the same as in larger turbines and noise generation is substantial.
Large wind farms are currently being constructed or planned which contain or will contain as many as hundreds of wind turbine generators each producing outputs in the megawatt range so that the total output of some of these farms may be in the hundreds or thousands of megawatts. On these farms the wind turbines are typically spaced specific distances apart. Where land area is sufficient, turbines are spaced three to five rotor diameters apart perpendicular to the prevailing wind, and five to ten rotor diameters apart in the direction of the prevailing wind, to minimize efficiency loss. The “wind park effect” loss can be as low as 2% of the combined nameplate rating of the turbines.
Because of large rotor diameters, the “foot print” required for these turbines is substantial. Noise generation requires substantial distance between turbines and residential housing. The energy conversion of prior art wind turbines is poor in the range of about 28 to 30 percent as stated above. Also, there is a “bird kill” environmental problem that is unavoidable with this size of wind turbine rotors operating at high blades tip velocities.
Therefore, there is a great need for a more compact, higher efficiency wind turbine systems, with greatly increased total wind turbines power output per occupied acreage, reduced noise generation and virtual elimination of the “bird kill” problem.